WASHINGTON -- Postmaster General William Henderson vigorously defended continuing talks between the U.S. Postal Service and FedEx Corp. to create a wide-ranging alliance, arguing that there is no legal basis to block such an agreement on antitrust grounds.

At a hearing of the House Subcommittee on the Postal Service, Mr. Henderson insisted that a deal to share express and ground deliveries between FedEx and the Postal Service wouldn't give the partners an unfair advantage over United Parcel Service Inc. and other competitors...